1. Field of the Invention
The present invention relates to a contact structure for connecting a circuit composed of a thin film transistor (hereinafter referred to as TFT) with a circuit over another substrate. Also, the present invention relates to a semiconductor device such as a display device utilizing such a contact structure. Especially, the present invention provides a technique that can be appropriately utilized for a liquid crystal display device and an electroluminescence (EL) display device that provided over one substrate a driving circuit set at a pixel portion and its periphery; a display device that formed together CPU, memory, data processing circuit, and the like over one substrate with the device; and furthermore, electronics that mounted these display devices. Note that, in the present specification, a display device refers to an overall display device that operate by utilizing a characteristic of a semiconductor, and not only the liquid crystal display device and the EL display device, but also the electronic device that mounted the display device are included into its category.
2. Description of the Related Art
Conventionally, the contact has been mainly formed in a laminated structure of a metal film and a protective conductive film over a substrate (for instance, Patent Document 1 can be referred) in the case of connecting electrically a connection wiring over a substrate with another wiring over a substrate by an anisotropic conductive film.
A method for connecting a substrate and a flexible printed circuit (FPC) is described using a cross-sectional view of a contact portion shown in the Patent Document 1. As shown in FIG. 3, an FPC 104 is formed of a substrate 105 and a wiring 106. A contact that laminates a metal film 102 and a protective conductive film 103 is formed over a substrate 101. An interlayer insulating film 109 and a protective film 110 are formed on a periphery of the contact to protect the metal film 102. The contact over the substrate 101 and the wiring 106 over the FPC 104 are connected by bonding using an anisotropic conductive film 107 that includes conductive particles 108.    [Patent Document 1] Japanese Patent Laid-Open No. 2001-93598
A circuit formed within a display device is performed an examination before bonding the FPC using an inspection apparatus to confirm operation of the display device in a process for manufacturing the display device. As shown in FIG. 6, an inspection apparatus 322 is composed of an external driving circuit 323 for driving a display device 311 with the purpose of inspecting; a measuring equipment 324 for measuring an electric characteristic of the display device 311; and an inspection electrode 321 for electrically connecting the display device 311, the external driving circuit 323, and the measuring equipment 324.
The inspection electrode 321 obtains an electric connection by physically contacting with a contact 120 formed on an FPC contact portion 316 over the display device 311. A signal line driving circuit 314 and a row select line driving circuit 315 formed within the display device 311 are driven using the external driving circuit 323 included in the inspection apparatus 322, and an electric characteristic of the signal line driving circuit and the row select line driving circuit 315 is measured using the measuring equipment 324 included in the inspection apparatus 322.
A contact by the conventional technique takes a structure that laminates the protective conductive film over the metal film in order to prevent corrosion and oxidation of the metal film. The protective conductive film has a high hardness; therefore, the damage of a contact surface due to a contact of the inspection apparatus 322 with the inspection electrode 321 can be prevented in the inspection during the process for manufacturing before bonding the FPC. However, the protective conductive film has high resistivity compared with that of the metal film; therefore, there is a problem that contact resistivity with the FPC gets higher and power consumption gets bigger in the condition of using the display device.